JPS6331100A - Sample holding circuit - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention samples an input signal and samples it for a predetermined period of time.
The present invention relates to a sample and hold (S&H) circuit that periodically generates a sampled output signal having a value equal to an input signal.

[Conventional technology]

In the conventional general S&H circuit shown in Figure 2, an input amplifier (1) is connected to a sampling switch (2) such as a diode bridge, and the sampling switch (2) is made to perform a gate operation. It includes a strobe pulse generator (3) which provides a sampling signal of the input signal to a hold capacitor (4). Stroop・
The waveform of the strobe pulse of the pulse generator (3) is
This is shown in Figure B. A signal obtained by sampling and holding the input signal is obtained from the hold buffer/amplifier (5) as shown in the waveform of FIG. 2A.

[Problem that the invention seeks to solve]

The conventional S&H circuit of FIG. 2 has a number of inherent limitations. First, in order to accurately charge the hold capacitor with the input signal, the switch resistance must be low and the charging efficiency must be high. However, when the switch resistance is lowered, an error due to leakage of the input signal called blowb due to capacitive coupling with the input signal occurs when the switch is turned off. The frequency bandwidth of the hold amplifier needs to be several times as wide as the maximum frequency bandwidth of the input signal due to the high frequency spectrum generated by the rectangular high frequency and large current Stroop pulse. Not only does it have to be a narrow high-frequency pulse, but it also has to have a large enough current value to charge the hold capacitor (4) in a short period of time. is causing the problem.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide an S&H circuit capable of high frequency sampling of input signals without the problems caused by rectangular high frequency, high current sampling pulses.

Another object of the invention is to provide an S&H circuit using analog technology that significantly reduces the cost of the circuit.

Another object of the present invention is to provide an S&H circuit using components that require a frequency band less than three times the frequency bandwidth of the input signal.

Another object of the present invention is to provide an S&H circuit that does not require expensive sampling switches that cause blow-by and fast, high current strobe generators that cause transient noise phenomena.

[Summary of the invention]

The aforementioned conventional problems are alleviated by the present S&8 circuit, which does not require high-frequency, high-current strobe pulses to sample human input signals. It includes a differentiator that receives a data signal as an input, and a multiplier that multiplies this differentiated input signal by a Strope signal.The product of this Strope signal and the differentiated input signal becomes the input of the differential amplifier together with the human input signal. , periodically generates a sample and hold signal of the input signal.

Since a high frequency and large current pulse is no longer required as a strobe signal, it is sufficient for the frequency bandwidth of the S&H circuit of the present invention to be at most three times the frequency bandwidth of the input signal.

Another advantage of the present invention is that the strobe signal may be a simple sine wave, thereby avoiding the problem of frequency bandwidth due to the high frequency spectrum that occurs in the case of rectangular high frequency, high current pulses. The output signal, which is the product of the strobe signal and the differentiated input signal, becomes the power of the differential amplifier together with the input signal. As a result, the slope of the output signal of this differential amplifier becomes a predetermined period O around each multiple of the sine wave Stroop signal period. When the slope of this output waveform becomes O, the output waveform has a value equal to the human input signal, holds this constant value for a short time, and outputs a waveform obtained by sampling the input signal.

〔Example〕

The input signal Va is input to the non-inverting input terminal of the differential amplifier (10). This manual signal Va is also manually differentiated by a differentiator (12) at the same time. This differentiated human power signal is applied to the multiplier (
14) and multiplied by the sine wave strobe signal Vs. The result of this strobe signal Vs and the differential signal of the input signal is input to the inverting input terminal of the differential amplifier (10). This output signal O1 indicates a signal equal to the value of the input signal for a certain period of time, and its sampling frequency is the frequency of the strobe signal.

When the input signal is Va, the output of the differentiator (12) is Va
'=dVa/dt. The frequency of the strobe signal Vs is fs, and the strobe signal Vs may be written as a sine wave signal as V so=sin (Jst). (
Here, ωs=2πfs. ) The sampling frequency of the S&H circuit of the present invention is the frequency fs of the strobe signal Vs.
becomes. The period Ts of the strobe signal Vs is Ts=2π/
It is ωS. The gain Am of the multiplier (14) is Am =
l/ω3 Vso, the output of the multiplier (14) is V
a'5in(Jst)/ωS. Therefore, the output Vo
is Vo = Va - Va' sin ((Jst) /
ωS...ill.

The human input signal Va is sampled at an integer multiple of the period 'Fs of the Stroop signal. (i.e., ]゛.

−n T s + where n represents a positive integer. )(1)
From the equation, the output signal V at the sampling time 'Fo.

(To) is Vo (”T'o) -Va (To)
It can be expressed as (If both sides of equation 11 are differentiated with respect to the equation, the following equation is obtained.

d Vo d Va dt dt In equation (2), when t='l''o=nTs, the second term on the right side is equal to the first term, so they cancel out, and the third
Since the term is O, the entire right side of equation (2) is zero.

Therefore, as shown by the basic function of S & H,
The slope dVo/dt of the output signal Vo is the sampling time T.
O becomes O.

FIGS. 3 and 4 illustrate the above explanation. In FIG. 4, the input signal Va is shown by a broken line, and the output signal Vo is shown by a solid line. In the vicinity of each time point that is an integral multiple of the period Ts of the Stroop signal, which is indicated by the numerical values 1 to 5 in FIGS. 3 and 4, the output signal ■.

The slope of is small during a period of 20 to 30% of the Stroop period Ts. Therefore, the output signal Vo is equal to the input signal Va at a time point corresponding to an integral multiple of the Stroop period Ts, and is also substantially equal during most of the Stroop period.

The terms and expressions used to describe the present invention do not limit the present invention in any way, and the present invention includes all equivalents to some or all of the contents disclosed herein. Therefore, it will be obvious to those skilled in the art that various changes may be made without departing from the spirit of the invention.

〔Effect of the invention〕

As described above, according to the present invention, there is no need for a highly accurate sampling switch (gate), a strobe generator, etc. as in the prior art, and it can be configured with a simple analog circuit, resulting in a significant reduction in cost. In addition, since a sine wave strobe signal is used instead of a rectangular high-frequency, large-current strobe pulse, there is no generation of transient noise.
Circuit components can be constructed with relatively narrow frequency bandwidths,
Furthermore, costs can be reduced. Furthermore, since no sampling switch (gate) is used, errors caused by blow pie can also be avoided. Furthermore, instead of holding each sampling value approximately constant until the next sampling using a hold capacitor as in the past, by obtaining a differential output between the input signal and the Stroop product signal, it is possible to obtain a signal that is more closely approximated by a human input signal. Accurate sampling waveforms can be easily obtained, and extremely significant effects can be observed.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an S&0 circuit according to the present invention, FIG. 2 is a block diagram of a conventional typical S&0 circuit, and FIG.
Figure A is a diagram showing the relationship between the human input signal and the output signal of the circuit in Figure 2, Figure 2B is a diagram showing the strobe signal of the circuit in Figure 2, and Figure 3 is a diagram showing the strobe signal of the circuit in Figure 1. 4 is a diagram showing the relationship between the human power signal Va and the output signal Vo for the concave road in FIG. 1. (10) is a synthesis means, (I2) is a differentiation means, and (I4) is a multiplication means.

Claims (1)

[Scope of Claims] 1. Differentiating means for differentiating an input signal; Multiplication means for inputting the output signal and Strope signal of the differentiating means; Synthesizing means for synthesizing the output signal of the multiplication means and the input signal. A sample-and-hold circuit characterized by comprising: 2. The sample-and-hold circuit according to claim 1, wherein the strobe signal is a sine wave signal. 3. The sample-and-hold circuit according to claim 1 or 2, wherein the combining means is a differential amplifier.